12.1.2.1 BPL outlines

You specify an outline in a BPL file as a sequence of straight
lines and cubic splines, in any order:

(outline start-xstart-ypiece1piece2...
)

start-x and start-y are realstrs which specify the initial
position for drawing this outline. Each successive piece of the outline
is relative to a current point, and also updates the current point.

At least one piece must be present. Each piece can be one of the
following two properties:

line xy. Draw a straight line from the current
point to (x,y). Then set the current point to (x,y).
x and y are realstrs.

spline c1xc1yc2xc2yexey.
Draw the Bezier cubic using the current point as the starting point,
(c1x,c1y) and (c2x,c2y) as the control
points, and (ex,ey) as the endpoint. Then set the
current point to the endpoint. All coordinates are realstrs.

If the last point the last piece of the outline is not the same
as the starting point, the result is undefined.